February 19 and 23, 2002 Meeting Notes
Joseph LaGrave (Sat)
Tuesday water cooled biprop engine tests
All of these tests were with the cat pack composed of 50 80
mesh silver screens alternated with 20 mesh stainless screens, with a spring
stainless anti-channel ring every 20 screens.
The pack continued to light up almost instantly through all tests, but almost
all the runs were rough.
The water cooled chamber has had the throat bored out to 0.375
from 0.25, in the hopes of increasing our mass flow enough so that we can move
up from the smallest (0.018) fuel jet, allowing us to bracket the rich/lean
area. The chamber was slightly deepened
to 3.125 to the top of the converging angle, and is 1.00 in diameter. Depending on if you count the converging
cone and the fuel injector ring, that give somewhere around an L* of 23, which
is a bit on the low side.
I took a few low quality videos this time.
I wanted to see how much we could possibly flow through the
cat pack, so we bolted the fuel injector ring onto the cat pack just as a
retainer, with no chamber or nozzle at all.
The results were interesting. It
took a lot longer than expected, showing that the 80 mesh screens are extremely
restrictive to gas flow, and that we arent likely to see much increased thrust
even though the new nozzle is over twice the area of the previous one. It was smooth for ten seconds, then very
rough for the last three seconds.
The exhaust was clearly subsonic, with the engine only
registering five pounds of thrust. The
retaining plate had 0.25 diameter holes in a 0.25 thick plate, so that was
not enough room for the gas to get to sonic velocity. We have run some motors in the past that worked ok with multiple
tiny nozzles, so I will probably make a thicker retaining plate with actual
converging / diverging cones the next time we try this.
0.120 peroxide orifice, no nozzle
0.060 peroxide 0.018 fuel, 250 psi
bad fuel solenoid connection
0.060 peroxide 0.018 fuel, 250 psi
solenoid worked, no fire
This was the exact combination that had worked well last
Saturday, but the larger throat seems to have changed the characteristics. Cat packs make scaling trickier, because a
change in chamber pressure will effect flow through the pack differently than
flow through the fuel orifice.
0.060 peroxide 0.020 fuel, 250 psi
rich? no fire?
0.060 peroxide 0.018 fuel, 250 psi
0.080 peroxide 0.018 fuel, 250 psi
0.070 peroxide 0.018 fuel, 250 psi
0.070 peroxide 0.022 fuel, 250 psi
We saw our cooling water jet burp steam on this run, so we
turned up the water flow for later runs.
0.070 peroxide 0.026 fuel, 250 psi
0.070 peroxide 0.030 fuel, 250 psi
some fire, rich cloud
This brackets the rich end of the burnable range.
0.070 peroxide 0.018 fuel, 250 psi, 475 peroxide 25 water
did not light
This was a test of reduced (85%) peroxide concentration,
which is reported to be necessary when using regenerative cooling and silver
screen catalyst packs. We need to get
this to light.
0.070 peroxide 0.018 fuel, 250 psi, undiluted peroxide
This was a long burn test.
Almost all of the runs were rough, but one or two were
smoother for no apparent or repeatable reason.
We measured our cooling water flow (after increasing it
after run 8) to be 450 ml of water flowing in 20 seconds, which is about how
much peroxide is flowing through the engine, so we arent far off from
something that could use the peroxide for regenerative cooling.
Saturday engine tests
We built a new catalyst pack with only 20 80 mesh silver
screens, then 30 20 mesh silver screens (still with stainless screens between
each silver screen). Because we are out
of fresh catalyst, all of these are from previously run engines. There were a couple noteworthy things when
the pack was taken apart:
The 80 mesh silver screen on the top had a neat hole punched
in it directly under the pipe fitting.
I had been leading with a silver screen as a minimum latency arrangement
for attitude engines, but after seeing this I have changed to leading with
stainless. This is also probably an
argument for a spreading plate, but the smoothest runs we ever saw were with a
screen pack with no spreading plate.
The 304 stainless spiral anti-channel rings had lost most of
their spring. They were still a tight
fit, and seemed to be doing the job, but no longer actively pressing against
the walls. After over five minutes of
hot fire, it probably isnt surprising.
If we find that we really do need the spring pressure, Smalley does
offer the spiral retaining rings in Inconel X-750.
Lists 304/316SS as good to 550 F
for springs, which is certainly exceeded by a good margin. The Inconel is listed as 750-1100 F max
temperature, which is still below what the lower rings will see, but would
certainly be an improvement.
I used new rings when rebuilding the pack.
Russ bored out the combustion chamber slightly from 1.0 to
1.1 diameter, which increases the L* from 23 to about 27. We were hoping this would help light with
the 85% peroxide.
Russ also made a completely new channel wall combustion
chamber to replace the simpler water jacketed chamber, but we didnt get around
to firing it today:
If it seals well and cools well, we will probably make a new
one out of aluminum and try full regenerative cooling with peroxide.
Matt was back, so we have some
good quality footage, but things werent running as well as they were the last
couple times. We also had a leaky
gasket on a couple of the early runs.
new cat pack: 20 x 80 mesh, 30 x 20 mesh
070 peroxide, 018 fuel
fire, rough biprop, moderately smooth monoprop
same, monoprop only
decently smooth, but not great
quarter inch more pack compression, adding a spacer. This was a LOT of pressure.
adjust feed line on the test stand to try to avoid theoretical
same, with fuel
not full decomposition?
reasonably smooth, didnt light
new battery for solenoid
we are out of kerosene, which is why the last run didnt
more kerosene in tank
difficulty lighting, but finally did catch for a rough run
replace pack spacer with 6 20 mesh silver + 7 stainless
screens to get a bit more active area
still had trouble lighting
We hooked up our ethane tank to see if we would have better
luck lighting a gaseous fuel. The
ethane tank was at 480 psi (Ethane is listed as 540
psi vapor pressure @ 70°F), which we regulated down. We knew we were going to need a lot larger orifice for the gas
than for kerosens.
ethane, 070 ethane at 300 psi, 070 peroxide
rough, did not light
480 psi ethane (max)
minor noticeable change, but probably still not rich enough
to light. The tiny solenoid is probably
the restricting factor for gas flow right now, so we will have to change to a
larger one when we try again.
back to the other all 80 mesh cat pack to repeat a run from
070 peroxide, 020 kerosene
barely lit, very rough
The all 80 mesh cat pack instantly warmed up on its first
run of the day, but it took a couple of tries to get the kerosene to light
today, while on Tuesday with these parameters, it would instantly light on
every push. We arent sure what is
going on with this. We are wondering if
the increased chamber diameter might actually be hurting the performance by
cooling the decomposed peroxide as it flows out of the narrower fuel injection
The mostly-20 pack is a lot
smoother than the all-80 pack, but still not nearly as smooth as the all-20
pack we tested a few weeks ago, and it doesnt seem to be getting 100%
decomposition. When our screen order
finally arrives, we will try to replicate the untra-smooth all-20 packs.
On January 5, we did our first spin test that just used a
single engine on a marginally balanced rotating hub. We have addressed several issues we had with that test:
The test stand has secure legs.
The rotor is increased to 1/4" stainless pipe from
1/8 to give more rigidity.
We have a pair of balanced engines.
We have a tachometer sensor on the shaft.
We mounted the tank directly above the rotary seal with an
AN-swivel union instead of a length of hose.
The test went flawlessly, and we let it spin up to just
under 500 rpm with brief pulses of peroxide.
The initial burst out of the engines was left over water
from the water test we ran before we loaded peroxide.
We are tilting the engines down a bit so it acts like the
rotor has more inertia, but it still doesnt have much of any drag, so it spins
up fast, and takes quite a while to slow down.
Our big rotor blades should be here any day now, but we will have to
reconfigure for spinning on top of our new vertical test stand, because it will
be 27 in diameter
This current configuration uses a hollow rotating shaft that
the peroxide flows through. This allows
an inexpensive axial rotary joint, but makes it impossible to mount a parachute
on the other side of the rotor, which we would like to do for the fast
vehicles. We are probably going to be
moving to an over-the-shaft rotary seal that would allow us to have a solid,
static shaft, with the tapered roller bearings mounted on the hub instead of
I was quoted $3100 for this in 316 SS, which is a bit
pricey, but it directly solves our problem.
The RPM range is going to be a little marginal on it, but we should get
by, because we will only need to see 500 RPM for a couple minutes at a time.
We need to get the tach sensor interfaced with a computer
and work on automatic RPM control.
There is a very long lag when turning the flow on and off, but I need to
get some actual graphs on the response rate, then try to auto-control it. Im not sure yet if we will use PWM on a
solenoid, or see if we can get one of our KZCO ball valves in 1/4".